Optical devices using LED such as a lighting system or display device have been used in a wide range of fields. Such an optical device comprises an LED element mounted on a circuit pattern on a substrate by electrically conductive adhesive, solder or the like with necessary wire connections by wire bonding, and a reflector (reflecting frame) provided around the LED element for enhancing the light utilization rate of LED, and the LED element located within the reflector being sealed by a translucent resin is used. As the white LED, various types are conventionally known, and such LED is generally adapted, for example, to obtain white light by combining a plurality of LEDs of green (G), blue (B), red (R) and the like, or to utilize the effect of wavelength conversion by mixing a fluorescent material to the sealing resin. For the wavelength conversion, blue LED is mainly used, but ultraviolet ray emitting LED is also usable as light source. As the reflector, a molding of a resin composition filled with white pigment particles composed of metal oxide may be used.
The reflector containing such resin composition is requested to have heat resistance to heating process of solder or the like for mounting the LED element on the substrate, heat generation during thermosetting of the sealing resin, heating for connecting an LED device to another member, heating in the use environment of the LED device, or the like, and to maintain a high reflectance during the subsequent period including usage. Further, the white LED is particularly requested to maintain a satisfactory reflectance in an area of 500 nm or less. From this point, a resin composition comprising a thermotropic liquid crystal polyester excellent in heat resistance, particularly, a wholly aromatic thermotropic liquid crystal polyester having a melting point exceeding 320° C. and white pigment has come to be used for the LED reflector (refer to, for example, Patent Documents 1 to 3).
Patent Document 1: Japanese Patent Kohyo Publication No. H6 (1994)-38520
Patent Document 2: Japanese Patent Application Laid-Open No. 2004-256673
Patent Document 3: Japanese Patent Application Laid-Open No. 2005-232210